Hexanoic acid production and microbial community in anaerobic fermentation: Effects of inorganic carbon addition

Carbon dioxide (CO 2 ) plays a crucial role in carbon chain elongation with ethanol serving as an electron donor. In this study, the impacts of various carbonates on CO 2 concentration, hexanoic acid production, and microbial communities during ethanol -butyric acid fermentation were explored. The results showed that the addition of MgCO 3 provided sustained inorganic carbon and facilitated interspecific electron transfer, thereby increasing hexanoic acid yield by 58%. MgCO 3 and NH 4 HCO 3 inhibited the excessive ethanol oxidation and decreased the yield of acetic acid by 51% and 42%, respectively. The yields of hexanoic acid and acetic acid in the CaCO 3 group increased by 19% and 15%, respectively. The NaHCO 3 group exhibited high headspace CO 2 concentration, promoting acetogenic bacteria enrichment while reducing the abundance of Clostridium_sensu_stricto_ 12. The batch addition of NaHCO 3 accelerated the synthesis of hexanoic acid and increased its production by 26%. The relative abundance of Clostridium_sensus_stricto_ 12 was positively correlated with hexanoic acid production.